Apparatus and methods for semiconductor IC failure detection

ABSTRACT

An improved voltage contrast test structure is disclosed. In general terms, the test structure can be fabricated in a single photolithography step or with a single reticle or mask. The test structure includes substructures which are designed to have a particular voltage potential pattern during a voltage contrast inspection. For example, when an electron beam is scanned across the test structure, an expected pattern of intensities are produced and imaged as a result of the expected voltage potentials of the test structure. However, when there is an unexpected pattern of voltage potentials present during the voltage contrast inspection, this indicates that a defect is present within the test structure. To produce different voltage potentials, a first set of substructures are coupled to a relatively large conductive structure, such as a large conductive pad, so that the first set of substructures charges more slowly than a second set of substructures that are not coupled to the relatively large conductive structure. Mechanisms for fabricating such a test structure are also disclosed. Additionally, searching mechanisms for quickly locating defects within such a test structure, as well as other types of voltage contrast structures, during a voltage contrast inspection are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part and claims priority ofU.S. patent application Ser. No. 09/648,380 (Attorney Docket No.KLA1P016B), entitled TEST STRUCTURES AND METHODS FOR INSPECTION OFSEMICONDUCTOR INTEGRATED CIRCUITS, filed Aug. 25, 2000, by Akella V. S.Satya et al., which application is incorporated herein by reference inits entirety for all purposes.

[0002] This application also claims priority of the U.S. ProvisionalApplication, having an application No. 60/329,804 (Attorney Docket No.KLA1P055P), entitled APPARATUS AND METHODS FOR SEMICONDUCTOR IC FAILUREDETECTION, filed Oct. 17, 2001, by Kurt H. Weiner et al., whichapplication is incorporated herein by reference in its entirety for allpurposes.

BACKGROUND OF THE INVENTION

[0003] This invention relates to methods and apparatus for detectingelectrical defects in a semiconductor device or test structure having aplurality of features that are specifically designed to produce varyingvoltage potentials during a voltage contrast inspection. Moreparticularly, it relates to voltage contrast techniques for detectingopen and short type defects within the features of the circuit or teststructure.

[0004] A voltage contrast inspection of a test structure is accomplishedwith a scanning electron microscope. The voltage contrast techniqueoperates on the basis that potential differences in the variouslocations of a sample under examination cause differences in secondaryelectron emission intensities when the sample is the target of anelectron beam. The potential state of the scanned area is acquired as avoltage contrast image such that a low potential portion of, forexample, a wiring pattern might be displayed as bright (intensity of thesecondary electron emission is high) and a high potential portion mightbe displayed as dark (lower intensity secondary electron emission).Alternatively, the system may be configured such that a low potentialportion might be displayed as dark and a high potential portion might bedisplayed as bright.

[0005] A secondary electron detector is used to measure the intensity ofthe secondary electron emission that originates from the path swept bythe scanning electron beam. Images may then be generated from theseelectron emissions. A defective portion can be identified from thepotential state or appearance of the portion under inspection. Theportion under inspection is typically designed to produce a particularpotential and resulting brightness level in an image during the voltagecontrast test. Hence, when the scanned portion's potential and resultingimage appearance differs significantly from the expected result, thescanned portion is classified a defect.

[0006] Several inventive test structures designed by the presentassignee are disclosed in co-pending U.S. patent application No.09/648,380 (Attorney Docket No. KLA1P016B), entitled TEST STRUCTURES ANDMETHODS FOR INSPECTION OF SEMICONDUCTOR INTEGRATED CIRCUITS, filed Aug.25, 2000, by Akella V. S. Satya et al., which application isincorporated herein by reference in its entirety. In one embodiment, atest structure is designed to have alternating high and low potentialconductive lines during a voltage contrast inspection. In one inspectionapplication, the low potential lines are at ground potential, while thehigh potential lines are at a floating potential. If a line that ismeant to remain floating shorts to an adjacent grounded line, both lineswill now produce a low potential during a voltage contrast inspection.If there is an open defect present within a line that is supposedlycoupled to ground, this open will cause a portion of the line to be leftat a floating potential to thereby produce a high potential during thevoltage contrast inspection. Both open and short defects causes twoadjacent lines to have a same potential during the voltage inspection.

[0007] Unfortunately, conventional voltage contrast test structures haveassociated disadvantages. For example, at least two photolithographymasking steps are required to fabricate these test structures. Onemasking step is required for creating the contacts to the substrate,which is grounded, and another masking step is required for fabricatingthe metal layer of the test structure which is being tested. The timerequired to fabricate a conventional voltage contrast test structurecould be important in some applications, such as using the voltagecontrast based test structures for quickly qualifying and/or monitoringa process tool's status.

[0008] Another more significant deficiency of the conventional voltagecontrast test structures is that they can only detect hard opens andshorts. This becomes an extremely significant issue, for example, in Cumetallization processing because a significant percentage of the defectsare partial opens. These partial opens, in vias or in metal lines, are areliability concern and also degrade the parametric performance of thesemiconductor chip.

[0009] Accordingly, there is a need for improved test structures whichmay be quickly fabricated. Additionally, there is a need for improvedtest structures in which partial open and short defects may be detected.

SUMMARY

[0010] In one embodiment of the present invention, an improved voltagecontrast test structure are provided. In general terms, the teststructure can be fabricated in a single photolithography step or with asingle reticle or mask. The test structure includes substructures whichare designed to have a particular voltage potential pattern during avoltage contrast inspection. For example, when an electron beam isscanned across the test structure, an expected pattern of intensitiesare produced and imaged as a result of the expected voltage potentialsof the test structure. However, when there is an unexpected pattern ofvoltage potentials present during the voltage contrast inspection, thisindicates that a defect is present within the test structure. To producedifferent voltage potentials, a first set of substructures are coupledto a relatively large conductive structure, such as a large conductivepad, so that the first set of substructures charges more slowly than asecond set of substructures that are not coupled to the relatively largeconductive structure. Mechanisms for fabricating such a test structureare also disclosed. Additionally, searching mechanisms for quicklylocating defects within such a test structure, as well as other types ofvoltage contrast structures, during a voltage contrast inspection arealso provided.

[0011] In one embodiment, a test structure that is designed for voltagecontrast inspection is disclosed. The test structure includes a firstsubstructure having a plurality of floating conductive structures thatare designed to charge to a first potential during a voltage contrastinspection and a second substructure that is coupled with a conductivestructure having a size selected to cause the second substructure tocharge to a second potential that differs from the first potentialduring the voltage contrast inspection. In one preferred embodiment, thefirst and second substructure are formed in a single photolithographystep.

[0012] In one implementation, the first and second substructure are notcoupled to the substrate. In another aspect, the first and secondsubstructure are both on a same level. In a specific embodiment, thesecond substructure includes a plurality of parallel strip segments thatare each adjacent to a one of the conductive lines of the firstsubstructure. In a further aspect, the second substructure forms aserpentine shape.

[0013] In another implementation, the second substructure is designed tocharge more slowly than the first substructure during a voltage contrastinspection. In another aspect, the second substructure is designed tohave a different intensity level than the first substructure during avoltage contrast inspection. Preferably, the conductive structure of thesecond substructure has a size selected so that a partial open may bedetected within the second substructure during the voltage contrastinspection. In an alternative embodiment, a method of fabricating one ormore of the above described test structure embodiments is alsodisclosed. The test structure is designed for voltage contrastinspection.

[0014] In another embodiment, the invention pertains to a method ofinspecting a test structure. Two or more initial portions of the teststructure are initially scanned with a charged particle beam todetermine whether there is a defect present within the test structurebased on whether there is an unexpected pattern of voltage potentialspresent within the test structure as a result of the initial scanning.When a defect is present, one or more potential defect portions of thetest structure are sequentially stepped to, and the one or morepotential defect portions of the test structure are scanned with acharged particle beam to thereby locate the defect.

[0015] In one implementation, the stepping is in the form of a binarysearch pattern for locating the defect. In another implementation, theoperation of initially scanning two or more initial portions of the teststructure with a charged particle beam to determine whether there is adefect present is accomplished by scanning a first end of the teststructure to obtain a first potential for the first end, scanning asecond end of the test structure to obtain a second potential for thesecond end, and determining that the test structure has an open defectwhen the first end potential differs from the second end potential.

[0016] In another aspect, the operation of stepping to one or morepotential defect portions of the test structure and scanning the one ormore potential defect portions of the test structure with a chargedparticle beam to thereby locate the defect includes a) stepping to afirst current portion of the test structure and scanning the firstcurrent portion of the test structure for a defect, b) when the defectis not found and a transition in intensity occurs between the previousscan and current scan, stepping to a next portion of the test structurethat is between the previous scan and the current scan, and c) when thedefect is not found and a transition in intensity does not occur betweenthe previous scan and current scan, stepping to a next portion of thetest structure that is not between the previous scan and the currentscan. In one aspect, the next portion is halfway between the previousand current scan when the defect is not found and a transition inintensity occurs between the previous scan and current scan, and thenext position is halfway between the current scan and an end of the teststructure that is not between the previous and current scan when defectis not found and a transition in intensity does not occur between theprevious scan and current scan. In a further aspect, it is determinedwhether the current scan includes a transition in intensity point forthe current scan that is not the defect, and the stepping to the nextportion operation is performed in a new direction when the current scanincludes the transition in intensity point that is not the defect. Inone implementation, the new direction of the next scan is perpendicularto a direction of the previous scan. In a specific aspect, operation (b)and (c) are repeated until the defect is found.

[0017] In one embodiment, the defect can be an open defect, and the opendefect is found when a transition in intensity occurs within the teststructure itself. In a further embodiment, the open defect can be apartially open defect. In another implementation, the defect can be ashort defect and the defect is found when a physical short is foundwithin the test structure.

[0018] In another embodiment, the invention pertains to an inspectionsystem for detecting defects within a test structure. The systemincludes a beam generator for generating an electron beam, a detectorfor detecting electrons, and a controller arranged to perform one ormore of the above described methods.

[0019] These and other features of the present invention will bepresented in more detail in the following specification of the inventionand the accompanying figures which illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a diagrammatic top view representation of a voltagecontrast image of a test structure in accordance with one embodiment ofthe present invention.

[0021]FIG. 2A is a diagrammatic top view representation of a voltagecontrast image of a test structure having an open defect in accordancewith one embodiment of the present invention.

[0022]FIG. 2B is a diagrammatic top view representation of a voltagecontrast image of a test structure having a short defect in accordancewith one embodiment of the present invention.

[0023]FIG. 3A illustrates a binary search mechanism for locating an opentype defect in a test structure in accordance with one embodiment of thepresent invention.

[0024]FIG. 3B is a flowchart illustrating a procedure for locating adefect in accordance with one embodiment of the present invention.

[0025]FIG. 4 is a diagrammatic representation of a system in which thetechniques of the present invention may be implemented.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0026] Reference will now be made in detail to a specific embodiment ofthe invention. An example of this embodiment is illustrated in theaccompanying drawings. While the invention will be described inconjunction with this specific embodiment, it will be understood that itis not intended to limit the invention to one embodiment. On thecontrary, it is intended to cover alternatives, modifications, andequivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

[0027] In general terms, one embodiment of the present inventionprovides voltage contrast based test structures that can be fabricatedin a single photolithography masking step and/or can be used to detectpartial opens. In one implementation, the test structure contains atleast two substructures. The two substructures are designed to producedifferent voltage contrast intensities without having to couple one ofthe substructures to ground (e.g., to the substrate).

[0028]FIG. 1 is a diagrammatic top view representation of a voltagecontrast image of a test structure 100 in accordance with one embodimentof the present invention. As shown, the test structure includes a firstsubstructure 102 that is coupled with a large conductive pad 110 and asecond substructure 104 formed from a plurality of floating conductivelines (e.g., 104 a through 104 g). Although the first substructure isdescribed as being coupled with a large conductive pad, of course, anysuitable conductive structure may be used that results in a differentpotential being produced in the first substructure during a voltagecontrast scan, as compared in the second substructure. Since the firstand second substructures are formed within the same conductive layer,the entire test structure may be fabricated with a singlephotolithography step. Photolithography techniques are well known tothose skilled in the art.

[0029] The large conductive pad 110 of the first substructure has a sizethat is selected to result in a different potential and intensity (i.e.,in secondary and backscattered electrons) when scanned with an electronbeam, as compared with the second substructure. That is, the largeconductive pad 110 is sized so that the first substructure to which itis coupled charges differently than the second substructure that is notcoupled to the pad 110. Different amounts of secondary or backscatteredelectrons are emitted from the differently charged portions of the teststructure in response to the incident electron beam. In the illustratedembodiment, the conductive lines 104 a through 104 g of the secondsubstructure charge quickly and produce a dark image during the voltagecontrast scan. In this case, the pad 110 is sized so that the firstsubstructure 102 charges more slowly than the conductive lines of thesecond substructure 104. Thus, the conductive pad 110 and the firstsubstructure 102 together have an area that is significantly larger thanthe area of a single one of the conductive lines (e.g., 104 a) of thesecond test structure. The size of the conductive pad 110 may bedetermined experimentally or by simulation. For example, increasingsizes may be used for various conductive pads of test structures todetermine whether the test structure's two substructures producedifferent potentials during voltage contrast inspection. Thus, the sizeof the conductive pad 110 may be selected to be equal to or greater thanthe smallest sized conductive pad 110 that experimentally produceddiffering potentials.

[0030] As an electron beam is passed over these substructures 102 and104 (e.g., in direction 106), the substructure 102 that is connected tothe large metal pad 110 has a potential that charges slowly compared toa structure that is not connected to a large metal pad. Thus, the largemetal pad acts as a virtual ground and appears bright, while thefloating conductive lines of the second substructure 104 appear dark.After the beam scans the substructure 102 for a period of time, thesubstructure 102 will approach the same potential as the secondsubstructure 104 that is not connected to the large metal pad. Hence,the voltage contrast difference is transient in nature. However, as anelectron beam is scanned initially, for example, in direction 206 alongwidth 208, the test structure appears as alternating dark and lightsubstructures when there is no defect present.

[0031]FIG. 2A is a diagrammatic top view representation of a voltagecontrast image of a test structure 200 having an open defect 204 inaccordance with one embodiment of the present invention. The teststructure 200 of FIG. 2 is similar to the test structure 100 of FIG. 1,except that the test structure 200 of FIG. 2 has an open defect 212.More specifically, the test structure 200 of FIG. 2 includes a firstsubstructure 202 that has the open defect 212 and a second substructure204 that does not include a defect. The first substructure includes afirst portion 202 a that remains coupled to a conductive pad 210 and asecond portion 202 b that is not coupled to the conductive pad 210.

[0032] Although transient in nature, one can detect an open defectwithin the first substructure 202. During a scan the portion 202 a ofthe first substructure connected to the conductive pad 210 has adifferent potential then the portion 202 b of the substructure 202 thatis not connected to the large conductive pad 110. Hence, the structuredisplays voltage contrast at the point of the physical break 212. Inother words, when an electron beam is scanned, for example, in direction206 along width 208, the test structure 200 does not have alternatingdark and light substructures as expected. The transient potentialdifference between the two different portions 202 a and 202 b of thefirst substructure may be characterized as an open defect.

[0033] The same principle can be employed for detecting partial openswith the first substructure 202. Partial opens increase the resistanceof the metal path. Consequently, under electron beam scanning, the pathsto the pad 210 that contain a partial open will develop transientpotential differences compared to the paths to the pad 210 which do nothave a partial open defect. This transient potential difference can bedetected as a transient voltage contrast signal. This transientpotential difference may be determined to be a partial open defect.

[0034] If the initial scan width 208 includes the defect, the specificlocation of such defect may then be determined by determining where thefirst substructure transitions between different potentials.Alternatively, if the initial scan width did not contain the defect, asecond scan may be required, for example, along a directionperpendicular to the first scan to determine the defect's specificlocation. Any suitable techniques for determining a defect's presenceand such defect's specific position may be utilized. Several defectpresence detection and defect location techniques are described inco-pending (1) U.S. patent application Ser. No. 09/648,380 (AttorneyDocket No. KLA1P016B), entitled TEST STRUCTURES AND METHODS FORINSPECTION OF SEMICONDUCTOR INTEGRATED CIRCUITS, filed Aug. 25, 2000, byAkella V. S. Satya et al., (2) U.S. patent application Ser. No.09/999,843 (Attorney Docket No. KLA1P037), entitled APPARATUS ANDMETHODS FOR MONITORING SELF-ALIGNED CONTACT ARRAYS, filed Oct. 24, 2001,by Kurt H. Weiner et al., (3) U.S. patent application Ser. No.10/000,114 (Attorney Docket No. KLA1P038), entitled APPARATUS ANDMETHODS FOR RELIABLE AND EFFICIENT DETECTION OF VOLTAGE CONTRASTDEFECTS, filed Jun. 29, 2001, by Kurt H. Weiner et al., (4) U.S. patentapplication Ser. No. 09/991,188 (Attorney Docket No. KLA1P045), entitledAPPARATUS AND METHODS FOR PREDICTING MULTIPLE PRODUCT CHIP YIELDSTHROUGH CRITICAL AREA MATCHING, filed Nov. 14, 2001, by Kurt H. Weineret al., and (5) U.S. Provisional Application, having an application No.60/329,804 (Attorney Docket No: KLA1P055P), entitled APPARATUS ANDMETHODS FOR SEMICONDUCTOR IC FAILURE DETECTION, filed Oct. 17, 2001, byKurt H. Weiner et al. These applications are incorporated herein byreference in their entirety. Additionally, other types of teststructures may be easily modified to implement the present invention.That is, any suitable voltage contrast type test structure may bemodified so that a first substructure is coupled with a relatively largeconductive structure, instead of being coupled to the substrate. Severalsuitable test structures are also described in detail in the abovereferenced patent applications (1) through (5).

[0035]FIG. 2B is a diagrammatic top view representation of a voltagecontrast image of a test structure 250 having a short defect 262 inaccordance with one embodiment of the present invention. As shown, thetest structure includes a serpentine substructure 252 coupled with alarge conductive pad 260. The test structure also includes a pluralityof conductive line substructures 254, which are designed to remainfloating or not coupled to the large conductive pad 560. However, ashort defect 262 has occurred between the serpentine substructures 252and the conductive line 254 c. During a voltage contrast scan indirection 256, the substructures are expected to have alternatingpotentials which result in alternating bright and dark lines. However,when two adjacent lines have a same potential, it is determined thatthere is a defect in one of the substructures. As shown, the conductiveline 254 c has the same potential and brightness level as adjacentstrips of the serpentine substructure 252. The short 262 may be found byscanning along direction 258.

[0036] In particular types of voltage contrast test structures, adefect's position may be determined by performing a search thatminimizes search time. In one embodiment of the present invention, adefect may be located by stepping to various locations on the teststructure, rather than continuously scanning along, for example, theentire length of the test structure. At each step location, the teststructure is scanned by the electron beam (e.g., rastered). This“accelerated search” technique may be implemented on any suitable teststructure, in addition to the above described test structures with largeconductive structures. One example of such an accelerated search is abinary search. Of course, any suitable search step may be utilized toquickly “step” to the defect's location in one or more steps. Forexample, the electron beam may be moved relative to the test structurein predefined incremental distances.

[0037]FIG. 3A illustrates a binary search mechanism for locating an opentype defect in a test structure 300 in accordance with one embodiment ofthe present invention. FIG. 3B is a flowchart illustrating a procedurefor locating a defect in accordance with one embodiment of the presentinvention. FIGS. 3A and 3B will be described in conjunction. The teststructure is grounded, for example, at target pad 302. Initially, it isdetermined whether an open defect is present with the test structure 300by scanning the structure with a charged particle beam in operations 352and 354. For example, the potential of target pad 302 is compared withthe potential of reference pad 308 during a voltage contrast inspection.When the pads differ in potential, it is determined that an open defectis present within the test structure 300. When the pads have the samepotential, it is determined that there is no defect present.

[0038] When it is determined that the test structure has no defectspresent, the procedure 350 ends. When a defect's presence is found, thecharged particle beam is stepped relative to the structure to a firstportion of the structure to scan for an open defect in operation 356.For example, it is determined whether there is a light-to-dark intensitytransition point in the test structure itself, which indicates an opendefect's location. In the illustrated embodiment of FIG. 3A, a binarysearch for the defect is first performed along the x direction. Althoughthe test structure is scanned along the top portion, any portion of thetest structure may be scanned during the search. The electron beam ismoved relative to the sample to location “1”, which is in the middle ofthe test structure 300 along the x direction. It is then determinedwhether an open defect has been found in operation 358. In theillustrated embodiment, it is determined whether the defect has beenfound by determining whether the transition point in the test structureitself has been found. If the defect has been found, the procedure ends.

[0039] If the defect has not been found, it is then determined whetheran intensity transition between dark and bright has occurred in the scandirection between the previous and current scan in operation 360. Thisdetermination is based on whether a transition point within the “scandirection” has been found, not whether the transition point has beenfound in the test structure itself. For example, the test structure mayinclude a dark portion immediately followed by a light portion along thex direction, but the transition point within the test structure itselfhas not been found yet.

[0040] If the transition point in the scan direction has not been foundyet, it is then determined whether there is a transition in the teststructure between the previous and current scan in operation 362. Forinstance, it is determined whether there is a transition between targetpad 302 and current scan location 1. If it is determined that there is atransition between the target pad 302 and location 1, then it isdetermined that the defect is to the left of or “behind” the searchlocation 1. In other words, it is determined that the defect is betweenthe previous (e.g., pad 302) and current scan (e.g., location 1). Thecharged particle beam is then stepped to “behind” the current scan to asecond portion of the test structure and this second portion is thenscanned for an open defect in operation 364. Otherwise, the chargedparticle beam is then stepped in “front of” the current scan to a secondportion of the test structure and this second portion is then scannedfor an open defect in operation 366.

[0041] The terms “behind” and “in front of” are used herein as aposition relative to the current stepping direction. For example, if thebeam has stepped from the test pad 302 to location 1 in a +x direction,the beam moves to a position “behind” location 1 when it is moved in the−x direction. In contrast, the beam moves to a position “in front of”location 1 when it is moved in the +x direction, which is in the samedirection as the current stepping direction defined by moving the beamfrom the pad 302 to location 1.

[0042] Since the transition does not occur between locations 1 and thetarget pad, the electron beam then moves relative to the test structureto a location 2 that is halfway between location 1 and the rightmost endof test structure (operation 364). The procedure then repeats operation358 to determine whether the defect has been found. In this example, itis determined that the defect has not been found. It is then determinedthat the transition point in the scan direction has not been found inoperation 360. It is then determined that the transition is between thecurrent scan and the previous scan in operation 362. As shown, atransition in brightness level has occurred between locations 1 and 2.The electron beam then moves relative to the sample to a location 3which is to the left of location 2 and halfway between locations 1 and 2to scan for an open defect (operation 364) at location 3. Since nodefect is found at location 3 and it is determined that the transitionis between location 3 and 1 (i.e., not between the previous and currentscan), the electron beam then moves to location 4 which is to the leftor “in front” of position 3 and halfway between locations 3 and 1(operation 362). The transition in the x direction is also found atlocation 4.

[0043] After the brightness transition is found in a first direction,the electron beam is then moved relative to the test structure in abinary search along the y direction to find the location of the defectin operation 368. As shown, the electron beam is first moved relative tothe test structure halfway down the length of the test structure tolocation 5. Since the brightness has transitioned between bright anddark from location 4 to 5, the next location 6 is halfway betweenlocations 5 and 4. The actual transition point in the test structureitself is found at location 6. It may then be determined that thetransition point is the location of the open defect.

[0044] In an alternative embodiment, a test structure may be scannedcontinuously in a first direction to detect the presence of a defect. Inthe test structure of FIG. 1, a charged particle beam is scannedcontinuously in direction 108. It is then determined whether there arealternating dark and bright of intensity levels for the conductivestrips of the test structure. An alternating pattern of intensitypattern indicates that there is no defect present. However, when twoadjacent strips have a same brightness level, it is determined thatthere is a defect present within on the adjacent strips having the samebrightness level. The defect's location may then be determined using astepping search algorithm, such as a binary search, along direction 106as described above with relation to FIGS. 3A and 3B. An open defect'sposition is found when there is a transition in a strip from dark tolight intensity value, or visa versa. A short defect is found when thephysical short is found between the two strips.

[0045]FIG. 4 is a diagrammatic representation of a scanning electronmicroscope (SEM) system in which the techniques of the present inventionmay be implemented. The detail in FIG. 4 is provided for illustrativepurposes. One skilled in the art would understand that variations to thesystem shown in FIG. 4 fall within the scope of the present invention.For example, FIG. 4 shows the operation of a particle beam with acontinuously moving stage. However, the test structures and productstructures and many of the inspection techniques described herein arealso useful in the context of other testing devices, including particlebeams operated in step and repeat mode. As an alternative to moving thestage with respect to the beam, the beam may be moved by deflecting thefield of view with an electromagnetic lens. Alternatively, the beamcolumn to be moved with respect to the stage.

[0046] Sample 1057 can be secured automatically beneath a particle beam1020. The particle beam 1020 can be a particle beam such as an electronbeam. The sample handler 1034 can be configured to automatically orientthe sample on stage 1024. The stage 1024 can be configured to have sixdegrees of freedom including movement and rotation along the x-axis,y-axis, and z-axis. In a preferred embodiment, the stage 1024 is alignedrelative to the particle beam 1020 so that the x-directional motion ofthe stage is corresponds to an axis that is perpendicular to alongitudinal axis of inspected conductive lines. Fine alignment of thesample can be achieved automatically or with the assistance of a systemoperator. The position and movement of stage 1024 during the analysis ofsample 1057 can be controlled by stage servo 1026 and interferometers1028. While the stage 1024 is moving in the x-direction, the inducer1020 can be repeatedly deflected back and forth in the y direction.According to various embodiments, the inducer 1020 is moving back andforth at approximately 100 kHz. Alternatively, a relatively wide beammay be used to scan across a particular swath or area of the teststructure without rastering of the beam.

[0047] A detector 1032 can also be aligned alongside the particle beam1020 to allow further defect detection capabilities. The detector 1032as well as other elements can be controlled using a controller 1050.Controller 1050 may include a variety of processors, storage elements,and input and output devices. The controller may be configured toimplement the defect detection and location techniques of the presentinvention. The controller may also be configured to correlate thecoordinates of the electron beam with respect to the sample withcoordinates on the sample to thereby determine, for example, a locationof a determined defect. In one embodiment, the controller is a computersystem having a processor and one or more memory devices.

[0048] Regardless of the controller's configuration, it may employ oneor more memories or memory modules configured to store data, programinstructions for the general-purpose inspection operations and/or theinventive techniques described herein. The program instructions maycontrol the operation of an operating system and/or one or moreapplications, for example. The memory or memories may also be configuredto store images of scanned samples, reference images, defectclassification and position data, as well as values for particularoperating parameters of the inspection system.

[0049] Because such information and program instructions may be employedto implement the systems/methods described herein, the present inventionrelates to machine readable media that include program instructions,state information, etc. for performing various operations describedherein. Examples of machine-readable media include, but are not limitedto, magnetic media such as hard disks, floppy disks, and magnetic tape;optical media such as CD-ROM disks; magneto-optical media such asfloptical disks; and hardware devices that are specially configured tostore and perform program instructions, such as read-only memory devices(ROM) and random access memory (RAM). The invention may also be embodiedin a carrier wave travelling over an appropriate medium such asairwaves, optical lines, electric lines, etc. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter.

[0050] Although the foregoing invention has been described in somedetail for purposes of clarity of understanding, it will be apparentthat certain changes and modifications may be practiced within the scopeof the appended claims. Therefore, the described embodiments should betaken as illustrative and not restrictive, and the invention should notbe limited to the details given herein but should be defined by thefollowing claims and their full scope of equivalents.

What is claimed is:
 1. A test structure that is designed for voltagecontrast inspection, comprising: a first substructure having a pluralityof floating conductive structures that are designed to charge to a firstpotential during a voltage contrast inspection; and a secondsubstructure that is coupled with a conductive structure having a sizeselected to cause the second substructure to charge to a secondpotential that differs from the first potential during the voltagecontrast inspection.
 2. A test structure as recited in claim 1, whereinthe first and second substructure are formed in a singlephotolithography step.
 3. A test structure as recited in claim 1,wherein the first and second substructure are not coupled to thesubstrate.
 4. A test structure as recited in claim 1, wherein the firstand second substructure are both on a same level.
 5. A test structure asrecited in claim 1, wherein the second substructure includes a pluralityof parallel strip segments that are each adjacent to a one of theconductive lines of the first substructure.
 6. A test structure asrecited in claim 5, wherein the second substructure forms a serpentineshape.
 7. A test structure as recited in claim 1, wherein the secondsubstructure is designed to charge more slowly than the firstsubstructure during a voltage contrast inspection.
 8. A test structureas recited in claim 1, wherein the second substructure is designed tohave a different intensity level than the first substructure during avoltage contrast inspection.
 9. A test structure as recited in claim 1,wherein the conductive structure of the second substructure has a sizeselected so that a partial open may be detected within the secondsubstructure during the voltage contrast inspection.
 10. A method offabricating a test structure that is designed for voltage contrastinspection, comprising: forming a first substructure having a pluralityof floating conductive structures that are designed to charge to a firstpotential when they are scanned with an electron beam; and forming asecond substructure that is coupled with a conductive structure having asize selected to cause the second substructure to charge to a secondpotential that differs from the first potential when it is scanned withthe electron beam, wherein the first and second substructures are bothformed within a single photolithography step.
 11. A method as recited inclaim 10, wherein the first and second substructure are formed in asingle photolithography step.
 12. A method as recited in claim 10,wherein the first and second substructure are not coupled to thesubstrate.
 13. A method as recited in claim 10, wherein the first andsecond substructure are both on a same level.
 14. A method as recited inclaim 10, wherein the second substructure includes a plurality ofparallel strip segments that are each adjacent to a one of theconductive lines of the first substructure.
 15. A method as recited inclaim 14, wherein the second substructure forms a serpentine shape. 16.A method as recited in claim 10, wherein the second substructure isdesigned to charge more slowly than the first substructure during avoltage contrast inspection.
 17. A method as recited in claim 10,wherein the second substructure is designed to have a differentintensity level than the first substructure during a voltage contrastinspection.
 18. A method as recited in claim 10, wherein the conductivestructure of the second substructure has a size selected so that apartial open may be detected within the second substructure during thevoltage contrast inspection.
 19. A method as recited in claim 10,further comprising inspecting the first and second substructures byscanning a portion of such substructures with an electron beam andobtaining a voltage contrast image of such scanned portion.
 20. A methodas recited in claim 19, further comprising determining whether there isa defect present within the first and/or second substructure based onthe voltage contrast image and when a defect is present, determining aposition of such defect by stepping the electron beam to variousportions of the first and/or second substructures.